Nuclear reactors are old and well-known in the art. Typically, the nuclear reactor has a nuclear core contained in a core barrel which is surrounded by a thermal shield designed to absorb the nuclear flux escaping from the nuclear core. The thermal shield is supported at circumferential points along its bottom and sides by the core barrel, but is radially spaced from the core barrel throughout most of its axial length. Because of the differential in temperature between the core barrel and thermal shield, these supports must be such as to provide for thermal contraction and expansion with temperature fluctuation during operation of the nuclear reactor.
The supports for the thermal shield have generally consisted of lower support blocks carrying most of the weight of the thermal shield, and upper displacement limiters toward the top of the shield designed to limit tangential movement of the shield relative to the core barrel. The lower supports are bolted and doweled to the core barrel, and the upper supports are keys extending through the thermal shield to engage grooves in spacer blocks positioned in the core barrel and the space between the core barrel and the thermal shield. These displacement limiters are designed to allow movement of the thermal shield relative to the core barrel typically of approximately 0.020 inch.
The difficulty is that with operation of the reactor the gaps in the displacement limiters have increased to up to as much as about 0.180 inch. These increased gaps in the displacement limiters cause fatigue and failure to the lower supports of the thermal shield jeopardizing continued safe reactor operation without repair.